The more I look at that U2 chip, the more I think my low-voltage idea might be correct… the touch screen is sending CTP_INT to the input of the U2 chip running at 3.3V, and if I am interpreting the CD74HC4050PWR data sheet correctly that means U2 is expecting about 2.4V for a HIGH and it's probably getting 1.53V (if VDDIO is floating on the GT911).

And that would in turn mean that I won't see anything, even 1.5V, at the “INT” pin on the screen module, right?

If VDDIO is tied to the 3.3V rail, though, I would expect signal at INT…

Update: The U2 chip from the display schematic seems to be a TI CD74HC4050PWR (https://www.ti.com/product/CD74HC4050/part-details/CD74HC4050PWR) which seems like it might be doing the level shifting between VDDIO and 3.3V? Just a shot in the dark, but it makes my theory a little less likely…

I don't know why all the links were stripped out of my post. Let me try again:

GT911 Datasheet: https://www.distec.de/fileadmin/pdf/produkte/Touchcontroller/DDGroup/GT911_Datasheet.pdf

DFR0669: https://wiki.dfrobot.com/3.5inches_480_320_TFT_LCD_Capacitive_Touchscreen_SKU_DFR0669

Second link is not working for some reason; pinout is here: https://docs.espressif.com/projects/esp-idf/en/latest/esp32/_images/esp32-devkitC-v4-pinout.png